The subject invention relates to an intumescent coating and manufacturing method therefor, in which the fire retardant coating produces a hard, vitreous, insulating char when exposed to heat and flame.
Intumescent coatings have been used in the past with mixed results. In particular, known fire retardant intumescent coatings tend to form a light, fluffy char that is highly susceptible to displacement from coated surfaces during turbulent air movements induced by a fire. This limits a coating's protectiveness and renders it unsuitable for use under certain fire conditions. Likewise, such unreliable performance results in an inability to consistently pass testing requirements.
Coatings that produce a hard char, capable of resisting turbulent air flow, typically contain organic solvents, cross linked organic polymers, and expensive polyphosphates or pyroposphates as a source of phosphoric acid. The resultant coatings, while generating a hard char, are expensive and often difficult to handle and apply.
Accordingly, there has been a long felt need for an inexpensive intumescent coating that resists removal by fire induced turbulence.
Flame resistant intumescent paints have been described (see, U.S. Pat. Nos. 4,198,328; 4,879,320; and 4,247,435). However, monoammonium phosphate has not been used in such coatings because it was thought to have unfavorable properties. Monoammonium phosphate is highly water soluble, which has the effect of causing it to leach out of the coating upon contact with water. When this occurs, no phosphoric acid is left to dehydrate the pentaerythritol and produce a carbon char. This motivated the art to teach away from the use of monoammonium phosphate, especially since improved durability was obtained from pyrophosphates and polyphosphates, such as the commercially successful PHOSCHEK 30 manufactured by Monsanto. Unfortunately, although pyrophosphates and polyphosphates produce water durable coatings, their decomposition temperature is such that a reduced amount of char is formed. This results in either reduced fire protection or the increased expense of using more material to achieve adequate protection.
The subject manufacturing method produces an intumescent coating with a strong, turbulence resistant char, water resistance and economic viability. This is possible by reacting orthophosphoric acid, melamine and monoammonium phosphate to effectively coat the monoammonium phosphate with a water resistant barrier. By employing such a reaction, the benefits of monoammonium phosphate can be obtained, together with the advantages associated with expensive polyphosphates.
Thus, the subject invention thus provides an unexpected advantage over known intumescent coatings and fulfills a long felt need for a cost effective intumescent coating.